a) Field of the Invention
The present invention relates to a magnetic disc driving motor and, more particularly, to a construction of a motor frame covering the bottom of the motor.
b) Background Art
A magnetic disc driving motor of the prior art is exemplified in FIG. 3. As shown in FIG. 3, a frame 1 is formed at its center integrally with a stationary shaft 2, and two ball bearings 3 and 3 are fixed on the outer circumference of the stationary shaft 2. On the outer circumferences of the ball bearings 3 and 3, there is fitted a hub 4 which has its center portion formed into a cylinder. This cylindrical central portion has its upper and lower end portions opened so that it may mount a magnetic disc (not shown) on its outer circumference. In the upper end opening of the hub 4, moreover, a magnetic seal 6 is fixed by an adhesive 7 for establishing a seal between the hub 4 and the stationary shaft 2 with a not-shown magnetic fluid so that the oil in the ball bearings 3 and 3 may not splash onto the mounted magnetic disc or the like.
The frame 1 is formed with a dish-shaped portion la which extends generally in a dish shape from the root of the stationary shaft 2. In the recess of the dish-shaped portion la, there is arranged a stator core 8 which has its inner end fixed on the lower portion of the stationary shaft 2. This stator core 8 is equipped with a plurality of projecting poles, each of which is wound with a coil 10. On the other hand, the stator core 8 has its outer circumference faced at a predetermined gap by the inner circumference of a rotor magnet 9 which is fixed on the inner circumference of the hub 4. Stator core 8, rotor magnet 9 and the like together constitute the motor, which is covered with the frame 1. As the rotor magnet 9 is rotationally driven, the hub 4 is integrally turned.
In the magnetic disc driving motor of the prior art described above, the frame 1 is integrally formed by cutting an aluminum material, for example, into the stationary shaft 2 and the dish-shaped portion 1a. When, however, this dish-shaped portion 1a is cut, this cutting is accompanied by a difficulty in reducing the thickness to a predetermined value or less due to the machining limit. This raises a serious problem in making a thinner motor. Moreover, when the frame 1 is to be cut, it is subject to a stress such as a chucking force for fixing it in the machine or a cutting force by the cutting tool. Thus, another problem arises in that the machining precision is deteriorated. Furthermore, since the cutting operation takes a long time, still another problem exists in that the cost for the parts is raised.